This application relates generally to communication systems, and, more particularly, to wireless communication systems.
Control signaling is necessary to support downlink and uplink transport channels. In Long Term Evolution (LTE) systems, Downlink Shared Channel (DL-SCH) and Uplink Shared Channel (UL-SCH) control signaling is utilized to support transport channels. The control signaling enables User Equipment (UE) to successfully receive, demodulate, and decode the DL-SCH. Downlink Control Information (DCI) is transmitted through a Physical Downlink Control Channel (PDCCH) and an Enhanced Physical Downlink Control Channel (EPDCCH). DCI includes information about the DL-SCH resource allocation (the set of physical resource blocks (PRBs) containing the DL-SCH), transport format and information related to the DL-SCH Hybrid Automatic Repeat reQuest (ARQ). A PRB includes a number of subcarriers by a number of symbols. In LTE, a PRB is twelve (12) subcarriers by seven (7) OFDM symbols, which is eighty-four (84) modulation symbols.
The DCI undergoes channel coding, the addition of a CRC attachment followed by convolutional coding and rate matching according to PDCCH format capacity, in order to form the PDCCH payload. The coded DCI bits (i.e., PDCCH payload) are then mapped to Control Channel Elements (CCEs) according to the PDCCH format. These coded bits are then converted to complex modulated symbols after performing operations including scrambling, Quadrature Phase Shift Keying (QPSK) modulation, layer mapping and precoding. Finally, the modulated symbols are mapped to physical Resource Elements (REs).
After performing deprecoding, symbol combining, symbol demodulation and descrambling at the receiver, the UE is required to perform blind decoding of the PDCCH payload as it is not aware of the detailed control channel structure, including the number of control channels and the number of CCEs to which each control channel is mapped. Multiple PDCCHs can be transmitted in a single subframe. All of these multiple PDCCHs may and may not be all relevant to a particular UE. The UE finds the PDCCH specific to it by monitoring a set of PDCCH candidates (e.g., a set of consecutive CCEs on which a PDCCH could be mapped) in every subframe. The UE uses its Radio Network Temporary Identifier (RNTI) to try and decode candidates. The RNTI is used to demask a PDCCH candidate's CRC. If no CRC error is detected, the UE determines that PDCCH carries control information for the UE.
A Machine Type Communication (MTC) device is a User Equipment (UE) that is used by a machine for specific application. For example, a MTC device could be associated with a water meter, electricity meter, or the like, and utilized to report usage measured by the meter. For instance, a MTC device could be a part of a health monitor and used to report a parameter or status of the health monitor. In LTE Rel-12, a Work Item (WI) on Low Complexity MTC (LC-MTC) UE was concluded where the complexity (cost) of the MTC UE was reduced by approximately fifty percent (50%). In LTE Rel-13, another WI was agreed to further reduce the complexity of MTC UE, to enhance the coverage and improve the power consumption of MTC UE. One of the complexity reduction techniques is to reduce the Radio Frequency (RF) bandwidth of the LC-MTC UE to 1.4 MHz (operating with 6 PRB). Herein, the term LC-MTC UE to refer to MTC UE operating in 1.4 MHz bandwidth.
A LC-MTC UE is expected to operate in any system bandwidth and shall be able to co-exist with legacy UEs. It is also expected that LC-MTC UE can retune its frequency to operate in different (1.4 MHz) sub-bands within the (larger) system bandwidth to allow frequency multiplexing among LC-MTC UE and also with legacy UE.